首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   304746篇
  免费   23088篇
  国内免费   14281篇
电工技术   24918篇
技术理论   51篇
综合类   39127篇
化学工业   34009篇
金属工艺   10605篇
机械仪表   16161篇
建筑科学   42989篇
矿业工程   16172篇
能源动力   15494篇
轻工业   16403篇
水利工程   14386篇
石油天然气   13328篇
武器工业   2957篇
无线电   18093篇
一般工业技术   21793篇
冶金工业   17329篇
原子能技术   3163篇
自动化技术   35137篇
  2024年   926篇
  2023年   2847篇
  2022年   5490篇
  2021年   6695篇
  2020年   7167篇
  2019年   5863篇
  2018年   5514篇
  2017年   6789篇
  2016年   7928篇
  2015年   8901篇
  2014年   17184篇
  2013年   15461篇
  2012年   20280篇
  2011年   21644篇
  2010年   17078篇
  2009年   17811篇
  2008年   16411篇
  2007年   21872篇
  2006年   20701篇
  2005年   18150篇
  2004年   15491篇
  2003年   14021篇
  2002年   11629篇
  2001年   9764篇
  2000年   8281篇
  1999年   6637篇
  1998年   4944篇
  1997年   4346篇
  1996年   3909篇
  1995年   3316篇
  1994年   2903篇
  1993年   2168篇
  1992年   1919篇
  1991年   1435篇
  1990年   1227篇
  1989年   1087篇
  1988年   862篇
  1987年   588篇
  1986年   444篇
  1985年   375篇
  1984年   358篇
  1983年   267篇
  1982年   235篇
  1981年   175篇
  1980年   143篇
  1979年   113篇
  1978年   66篇
  1977年   74篇
  1976年   58篇
  1975年   57篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Buffalo milk Cheddar cheese samples of different ages were analysed for compositional attributes (CA), ripening indices (RI) and Instron Textural Profile (ITP). All samples were compositionally alike, except for pH and salt-in-moisture (SM) contents. RI showed significant variations. CA and RI showed highly significant correlations within themselves and with each other, except for moisture with pH, SM with moisture, MNFS, Fat and FDM and Fat with MNFS. The ITPs of cheeses showed significant variations and had highly significant intercorrelations indicating their interdependence. CA (except moisture and MNFS) and RI showed a highly significant correlationship with ITPs. Moisture content showed a highly significant correlationship with all ITPs, except cohesiveness and springiness, where it was significant. MNFS content showed significant correlations only with hardness and brittleness. Stepwise regression analysis revealed that MI was the most predominant factor influencing cheese texture, followed by pH, SM, FDM and TVFA. Knowing Ca and RI, the textural properties of cheeses can be forecast through mathematical equations. Similarly the age of cheese can also be predicted if RI and/or textural properties are known.  相似文献   
42.
Packaging engineers need to be able to accurately determine the forces present in the shipping environment in order to protect packaged goods. The purpose of this study was to determine the vertical vibration levels measured in three separate truck-trailer suspension systems; conventional leaf-spring, conventional air-ride and damaged air-ride. The main conclusion reached in this study is that the air-ride suspension when maintained gives lower power density (PD) levels on all road surfaces studied. A damaged air-ride suspension and leaf-spring suspension are very similar in response frequencies, although the damaged air-ride produces higher vibration levels at lower frequencies.  相似文献   
43.
What has become known as Community Operational Research has been around in the UK for many years. The election of Jonathan Rosenhead as President of the UK OR Society in 1986–87 was the catalyst for bringing together and expanding activities which had been carried out largely by individuals working in isolation on a voluntary basis. The following five years have seen the establishment of the Community OR Unit at Northern College, the Centre for Community OR at Hull University and the Community OR Network, which supports the activities of volunteer OR workers across the UK. This paper reviews the range and types of work which have been undertaken by various practitioners. An assessment of the success of community OR is made and a number of issues which have arisen are discussed. Finally, given the diverse nature of community OR, its practice and practitioners, there is some discussion about the future of the area.  相似文献   
44.
立式平管板U形管束的压水堆核电站蒸汽发生器安装至瞬变工况期间,管板上表面的铁基金属残余物的堆积和外来物的存在,以及商业运行后管板、传热管、管子支撑板等的低流速区域里沉积物的堆积要求进行蒸汽发生器的清洁度检查。介绍了蒸汽发生器二次侧清洁度的视频检查技术。该技术适用于蒸汽发生器安装至瞬变工况和投入商业运行后可能发生污染的各阶段的清洁度检查。  相似文献   
45.
The hydrolysis of isocyanic acid in the gaseous phase has been investigated at temperatures between 553 and 613 K by mass spectrometry and evaluated to obtain the corresponding kinetic data. The reaction order and reaction constant have been determined. Finally, the influence of water on the catalysed formation of melamine from isocyanic acid under the operating conditions employed has been investigated in order to determine whether there is a need to try the process gas.  相似文献   
46.
47.
《Drying Technology》2007,25(12):1949-1958
A mathematical model for through drying of paper at constant pressure drop was developed. The model is based on physical properties; hence, basis weight, pressure drop, drying air temperature, pore size distribution, initial gas fraction, and tortuosity are important input parameters to the model. The model was solved for different combinations of the variables basis weight, drying air temperature, and pressure drop corresponding to industrial conditions and the results were compared with data from bench-scale experiments. The simulations show that the drying rate curve is very sensitive to the air flow rate and that correctly modeling the correlation between pressure drop and air flow rate is the most important factor for a successful model for through drying. The model was tuned by adjusting the parameters initial gas fraction and tortuosity in order to give the best possible fit to experimental data. For a given basis weight and pressure drop, different drying air temperatures resulted in relatively constant values of the fitted parameters. This means that the model can well predict the effects of changes in drying air temperature based on a tuning of the model performed at the same basis weight and pressure drop. However, for a given basis weight, an increase in pressure drop yielded fitted parameters that were somewhat different; i.e., a lower initial gas fraction and a higher tortuosity, a change that increases the resistance to air flow. This implies that the correlation between pressure drop and air flow rate in the model does not quite capture the nonlinear relationship shown by the experiments.  相似文献   
48.
In order to control a project, construction management requires project information. This is obtained through accounting, estimating, cost management and scheduling functions which produce project reports. These reports are best obtained by subdividing the project into small parts. The ways in which each of these functions subdivides a project in order to produce its reports is discussed, together with a means of interrelating this information with a technique known as the work breakdown structure.  相似文献   
49.
50.
支气管上皮靶细胞形态学参数对计算受氡子体照射的支气管的剂量是很重要的。本文介绍利用奥尔新兰-PAS 染色的外科切除人肺组织切片,测量基底细胞粘液细胞和的胞核深度与数目。结果表明,叶、段和小支气管的粘液细胞核深度分别为相应节段基底细胞的61%、69%和73%;此三节段粘液细胞的数目分别为基底细胞的53%、29%和28%,平均为37%。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号